1. Field of the Invention
This invention relates to the field of continually variable cone-pulley, belt-drive transmissions, particularly to a spring loaded device for moving pulleys on primary and secondary shafts.
2. Description of the Prior Art
The continually variable belt-drive transmission described in British Pat. No. 1,200,668 includes a primary shaft supporting a stationary cone-pulley and an axially displaceable cone-pulley, and a secondary shaft driven by an endless drive belt from the first shaft supporting stationary and axially displaceable cone-pulleys. The movable cone-pulleys include cylinder jackets and piston discs secured to the corresponding shafts to form pressure fluid servos for hydraulic displacement of the movable pulleys. One spring assembly located in each servo applies a minimum preload to the drive belt. A similar transmission, described in German Offenlegungsschrift No. 29 48 195, includes a spring assembly located in the fluid Pressure servos wherein the spring assembly includes a large Belleville spring.
These transmissions have the disadvantage that axial displacement of the pulley caused by action of the spring is only a very short distance because of the short path of travel of the spring. As a result, the control range of the transmission is unacceptably small. When a helical compression spring of large size is provided, the magnitude of the preload developed in the spring is too small to permit a motor vehicle to be driven by a continually variable transmission.
A continually variable transmission described in German Offenlegungsschrift No. 31 17 657 includes a spring located in the pressure fluid servo located on the secondary shaft, but no spring is present in the pressure fluid servo of the primary shaft. Assembly of the drive belt and the sun gear forming the input member would be impossible to complete in mass production if spring-actuated pressure fluid servos were included on both the primary and secondary shafts.